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content of tomatoes, is evidence that no appreciable loss of vitamin C could have occurred during the process of preparing them. No available evidence indicates any appreciable loss within periods of distribution of vitamin C in canned foods in general, or in canned tomatoes or tomato juice in particular. The process by which the three experimental batches of tomato juice were made is so simple and operation by it so inexpensive that it should be a means for producing commercial tomato juice with a vitamin content practically equivalent to that of the raw tomatoes from which it was made. It is entirely possible to combine a vacuum process, substantially similar to that previously described, with this process. The vacuum would only need to be very small as compared with tomato juice that is not subjected to any heating process. This affords a means to avoid heating the juice higher than pasteurizing temperatures for those who feel superior flavor is thus obtained. The heating element alone or the extraction apparatus as well may be enclosed in the vacuum chamber. Enclosing the extraction apparatus in a vacuum chamber involves complications in the way of intake and outlet
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valves, respectively, for the tomatoes and refuse. A barometric leg of short length would be adequate to permit the juice to emerge automatically at the temperature to which it would be heated.
LITERATURE CITED (1) Hess, A. F., "Scurvy Past and Present," Lippincott, 1920; Givens, M. H., and McCluggsge, H. B., Proc. SOC.Exptl. Bid. M e d . , 18, 164 (1921); La Mer, V. K., Dissertation, Columbia University, 1921; Dye, Marie, C a n n i n g Trade, 50, No. 35, 14 (1928) ; House, M. C., Nelson, P. M., and Haber, E. S., J.Bid. Chem., 81, 495 (1529); Clow, Bertha, and Marlatt, A. L., J. A g r . Research, 40, 767 (1530). (2) Hess, A. F., and Unger, L. J., Proc. SOC.Exptl. Bid. Med., 16, l(1518); Am. J. Diseases Children, 17, 221 (1919). (3) Kohman, E. F., Canner, 74, No. 24 (1931); Food I n d . , 3, No. 6 , 263 (1931); C a n n i n g A g e , 12, No. 7, 424 (1931); Western Canner & Packer. 23. No. 2. 7 (1931). (4) Kohman, E. F., Eddy, W. H., a n d Zall; Celia, IND. ENG.CHEM., 22, 1015 (1930). RECEIVEDMarch 17, 1933. Presented before the Division of Agricultural and Food Chemiatry a t the 85th Meeting of t h e American Chemical Society, Washington, D. C., March 26 to 31, 1933.
Temperature Coefficient of Vulcanization TI. Determination for Mixes Accelerated with Tetramethylthiuram Disulfide and a Butyraldehyde-Aniline Condensation Product' R. V. SANDSTROM, Municipal University, Akron, Ohio Temperature coeficients are determined f o r stocks whether the coeficient changes in this range. The accelerated with tetramethylthiuram disulfide and values obtained f r o m modulus and combined sulfur with a butyraldehyde-aniline condensation product. data are found to be 1.438 and 1.548, respectively, Cures are made at 10" intervals f r o m 310" to f o r tetramethylthiuram disuljide, and 1.672 and 220" F., and also in a constant-temperature oven 1.625, respectively, f o r the butyraldehyde-aniline in a bolted mold at 210", 18fi", and 160" F. The condensation product ( f o r 10" F. intervals). T h e lower temperature cures are made to determine coeficients do not change at the lower temperatures.
I
N 1902 Weber (7") stated that if two different specimens of vulcanized rubber from the same batch of crude rubber possess the same coefficient of vulcanization, it by no means implies that the two specimens also possess the same physical constants. He said that the amount of work done on the rubber and also the temperature and duration of the vulcanizing period are factors which influence the physical constants of the finished product. Other workers have also found this to be true. Weber also pointed out that the rate of cure increases with rise in temperature. Up t o the present there has been a wide range in temperature coefficients obtained by different men using different methods of determination. The values range from 8" to 25" F., an average of 15' F. being selected as the rise in temperature which would double the rate of cure. Some results obtained by previous workers are given in Table I.
DETERMINATION O F T E M P E R 4 T U R E COEFFICIENT Coefficients of vulcanization were determined by both physical and chemical data. With the physical data for a given stock it was assumed that, where there was equal modulus, there was equivalent cure. With the chemical data for a given stock it was assumed that, where there was 1
For Part I see reference
(4).
the same coefficient of vulcanization, there was equivalent cure. TABLE I. TEMPERATVRE COEFFICIENTS~ TEWP.TO D-OUBLE RATEO F
TYPEO F S T O C K A N D ACTHOR MEANS O F DETERMINATIONCURE F. A . 0. Bourn Litharge accelerated 20-21 Spence and Young Pure gum stock: com12.8 bined sulfur A. 0. Bourn Physical properties 11 A. Van Rossem Combined sulfur 18 Twiss and Brazier Combined sulfur 15 Extensibility a t given elongation 15 Time to reach maximum tensile 14.2 J. R. Sheppard Free sulfur 13.1 Hand tear, modulus, C. R. Park (S) and combined sulfur .. Park and MaxMercaptobenzothiazole accelerated; mqdulus .. well ( 4 ) MercaDtobensothiaaole accelerated: combined sulfur .. Crotonaldehyde-aniline accelerated. modulus .. Crotonaldehyhe-aniline accelerated; combined sulfur .. a
Part of the d a t a are taken from Sheppard ( 5 ) .
FACTOR BY WHICH RATEIs MULTIPLIED W H E N
TEMP.I S RAISED' 10' c. 10' F. 1.8
1.37
2.65 3.1 2.0 2.3 2.3
1.72 1.87 1.47 1.59 1.59
2.4 2.59
1.63 1.70
2.5
1.66
1.91
1.43
2.30
1.59
2.32
1.60
2.67
1.T3
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FIGURE1. MODULUS-TIME DATAFOR STOCKI Tetramethylthiuram disulfide is commercially known as Tuads, the butyraldehyde-aniline condensation product as du Pont's "808.." COMPOUKDING.Two stocks were prepared as follows: 1 50.0 50.0 5.0 3.0 0.2
Smoked sheet Pale crepe Zinc oxide ( X X Red Horsehead) Sulfur Tuads 808"
..
I1 50.0 50.0 5.0
3.0 0:5
The rubber, zinc oxide, and sulfur were master-batched on a factory mill, sufficient stock for all the experimental work being milled a t one time. The accelerator was weighed on a piece of rubber on a n analytical balance and incorporated on a n experimental mill. The stock was sheeted off and allowed to stand overnight before curing.
DATAFOR STOCKI1 FIGURE2. MODULUS-TIME CHEMICALTESTING.The rest of the cured sheets was saved for the determination of combined sulfur. I n order to obtain the true combined sulfur, the Kelly method ( 2 ) was used. Kelly stated that, in vulcanized rubber, sulfur appears in two forms as follows: A cetone-soluble
Free sulfur Sulfur united with resins, organic accelerators, proteins, and antioxidants Acetone-insoluble Sulfur in union with rubber Sulfur in union with resins, accelerators, proteins, etc. Sulfur in union as sulfides Sulfur in union as sulfates I n these tests, the sulfur in union with rubber was the form investigated. Two-gram samples were acetone-extracted overnight in an Underwriter's flask. This eliminated the acetone-soluble sulfur. To eliminate the acetone-insoluble sulfur in combination with resins, etc., the samples were boiled with alcoholic potash for 4 hours to saponify these resins and thereby free the sulfur. The sulfur was washed out by boiling with water for 2 hours. To free the sample from sulfide sulfur, a saturated hydrochloric acid-ether solution rTas added and allowed to stand for an hour. The sample was placed in a 250-cc. beaker, and 5 cc. mater were added. About 50 cc. of a nitric acid-bromine mixture were Yo
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FIGIJRE 3. TIME-TEMPER4TURE CURVES FOR MODULUS DATA .4.
Stock I
B.
Stock I1
CURIKGAND PHYSICAL TESTING.The stock was cured in a small Knox-screw press. The temperature mas checked by a press standardizing block as suggested by the Physical Testing Committee of the Division of Rubber Chemistry (6). This block was used every time the temperaturf1 was changed, and made it possible to hold the temperature within *0.2' F. of the point desired. A series of cures was made in the press a t intervals of 10' F. (5.5' C.) starting a t 310' F. (154.4' C.) down to 220" F. (104.4' C.). Cures were also made in a bolted mold in a constant-temperature oven a t 210" F. (98.9" C.), 185' F. (85' C.), and 160' F. (71.1" C.). The object of the lower temperature cures was to determine whether the coefficient changed in this range. Two 0.25-inch dumb-bell test strips were died out from sheets approximately 0.075 inch in thickness. They were tested on a Scott testing machine by the two-observer method. Modulus (at 300, 500, and 700 per cent elongation), tensile, and elongation were plotted. All data were obtained in pounds per square inch and then converted to kilograms per square centimeter.
PZ 18 14
IO
6 2
FIGURE4. PERCESTAGE COMBINED SULFUR-TIME DATA FOR STOCK 1 added slowly and allowed to digest for an hour in the cold, after which the volume was reduced to about 20 cc. A few crystals of potassium chlorate were added, and the solution was evaporated to dryness. Concentrated hydrochloric acid was added and evaporated to dryness t o expel nitric oxide fumes. This was repeated until complete expulsion was accomplished. The sulfate was then precipitated and ignited in the usual way.
DISCUSSION OF RESULTS As Park and Maxwell (4) point out, modulus may be determined with greater accuracy than other physical properties
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The observations made here agree with Cranor (1) who showed that coefficient, of vulcanization is not an index of the physical state of cure. The coefficients found check closely to those observed by Park and Maxwell (Table I). Mold lag was disregarded in this work because, in the opinion of the author, mold lag had very little effect upon the final results. As far as the writer was able t o detect, there was no change in the temperature coefficient a t the lower temperatures. Much difficulty was experienced in obtaining uniformity in the strips owing to the variations in the pressure in the
52
FIGURE5 . PERCENTAGE COMBINED SULFUR-TIME DATAFOR STOCKI1 which are sometimes used to determine temperature coefficients. The elongation is arbitrarily chosen. For this determination 700 per cent eIongation has been used. The modulus values read from the stress-strain curves a t 700 per cent elongation were plotted as modulus-time curves as shown in Figures 1 and 2. At each temperature the time to produce a given modulus was read from the charts, assuming that a t the same modulus we have equivalent cures. In Figure 1, showing data on stock I (Tuads), the modulus of 90 kg. per sq. cm. was used; in Figure 2, showing data on stock I1 (LY308”),60 kg. per sq. cm. was used. These times were plotted on semilog paper (Figure 3) and the coefficients calculated. The same method was used with the combined sulfur data. The percentage combined sulfur was plotted against time as shown in Figures 4 and 5. At each temperature, the time to give the same percentage of sulfur was read. Here it was assumed that, when we have the same coefficient of vulcanization, we have equivalent cures. These times were plotted against temperature as in the case of the modulus data (Figure 6). The temperature coefficients were calculated to be as follows: STOCK 1
STOCK I1
The coefficient obtained from combined sulfur data for T u a d s - a c c e l e r a t e d stock is higher than that obtained from the physical data. W i t h t h e ‘%08”-accelerated stock t h e r e e,o was very little difference. 180
Y
I
